This invention relates to an electrical connector to be mounted mainly on a main body, control box or the like of a machine tool, servomotor, robot or the like.
FIGS. 1a and 1b illustrate a circular connector as one example of hitherto used electrical connectors in a sectional view and a side view seen from the fitting side (on the right side of FIG. 1a) of the connector, respectively.
Referring to FIG. 1a, a plug shell 11 is cylindrical and provided on its outer circumferential surface with a key 111 extending in a longitudinal direction on the fitting side. The outer circumferential surface of the plug shell 11 provided with the key 111 is adapted to be fitted in an inner bore of the receptacle shell of a receptacle connector (not shown) mating with this plug shell 11.
An insert block 142 having contacts 141 held and fixed thereto is mounted in and fixed to an inner bore 112 of the plug shell 11 by means of an annular anchoring spring 143. FIG. 1a illustrates only two contacts 141 on the sectional plane of the drawing and other contacts are not shown.
These contacts 141 are adapted to contact mating contacts (usually socket contacts) provided in the receptacle connector (not shown) to establish an electric connection.
Moreover, the plug shell 11 is provided on the outer circumferential surface with a flange 113.
A coupling ring 12 cylindrical in shape surrounds the plug shell 11 and is provided on the fitting side (on the right side of the drawing, FIG. 1a) with fitting means 121 (a single thread screw in this embodiment). This fitting means 121 is adapted to fit with fitting means provided on the receptacle shell of the receptacle connector (not shown).
The coupling ring 12 is formed with a circumferential groove 122 in which a retainer ring 13 as a C-shaped washer is fitted. The retainer ring 13 is fixed snugly in the circumferential groove 122 so that the retainer ring 13 does not wobble with any external disturbance. When the coupling ring 12 is fitted in the mating receptacle connector and is being moved toward the receptacle connector, the retainer ring 13 abuts against the rear end of the flange 113 (on the left side of the flange 113 in the drawing) to transmit urging force (thrust) to the flange 113 as a flange urging portion.
The flange 113 is accommodated between the retainer ring 13 and a shoulder 123 formed in the coupling ring 12 with some play or clearance. Therefore, the coupling ring 12 is rotatable relative to the plug shell 11 to facilitate the insertion of the plug shell 11 into the mating receptacle connector and the engagement of the fitting means 121 with the fitting means of the receptacle connector. With the coupling ring 12 rotatable when free from the mating receptacle connector in this manner, the threaded engagement of the fitting means can be started by manually rotating the coupling ring 12 relying upon the manual touch an operator in order to connect the plug and receptacle connectors. Consequently, this arrangement is one advantage for the connectors which are frequently arranged in narrow spaces between appliances.
A back shell 15 is a cylindrical cover for protecting connections (on the left ends of the contacts in FIG. 1a) of electric wires (not shown) connected to the contacts 141. The back shell 15 is integrally fixed to the plug shell 11 with the aid of pipe threads formed on the outer circumference of the rear end (on the left end) of the plug shell 11.
In the prior art, a single thread screw having a relatively small pitch has often been used as the fitting means 121 because it is preferable for connectors requiring large thrust. In more detail, there is a relation f.varies.T/P where f is thrust, T is torque to be applied to the coupling ring 12 and P is a pitch of screw. On the other hand, the torque T can be manually set at substantially constant valued from 15 kg-cm to 20 kg-cm. Therefore, the smaller the pitch P of screw, the larger is the thrust to be obtained.
In connectors, however, a certain length of fitting between the connectors is needed so that the plug shell must be moved forward at least through the fitting length for proper fitting of the connectors. Accordingly, if the pitch of screw is small, the number of rotations of the coupling ring becomes large so that operation of the coupling becomes difficult.
In electrical connectors, moreover, there are many cases where the required thrust is not very large depending upon number, configuration and construction of contacts. In such cases, it may be desirable to provide screws having large pitches.
If the pitch of a screw is large, the rotating number of a coupling ring becomes advantageously less. However, the screws with large pitches are likely to unscrew due to vibration and the like. Therefore, they encounter a new difficulty of increased chance of disconnection of connectors mating.
In connectors, furthermore, it is sufficient to advance a plug shell through a predetermined distance (more than a fitting length) as a design value of the connector and fix it thereat, whereas the completion of the advance of the plug shell through the predetermined distance with the aid of screw can be detected only by change in torque applied to the coupling ring. Therefore, it is not an easy matter to detect whether the coupling ring has been advanced to the fullest extent.
FIG. 2 illustrates another example of hitherto used electrical connectors. This connector includes a receptacle connector 1B' having a pin contact a secured to an insulator b, and a plug connector 1A' having a socket contact c provided in an insert aperture e of a base insulator d. In this case, the receptacle connector 1B' is directly connected to the plug connector 1A'.
The plug connector 1A' is called a front release connector, whose socket contact c can be disconnected from the pin contact a of the receptacle connector 1B' by operation on the fitting side with the receptacle 1B'.
This disconnection will be explained referring to FIG. 2. A cylindrical removing jig (not shown) is inserted through the fitting portion of the receptacle connector 1B' into a clearance between the inner wall of the insert aperture e and the socket contact c so that an anchoring tongue f of the socket contact c is deformed inwardly to disengage from an anchoring step g formed on the inner wall of the insert aperture e. Under this condition, therefore, by pulling a cable h connected to the socket contact c rearward, the socket contact c is removed from the insert aperture e.
With the plug connector 1A' of the front release connector, however, an opening of the insert aperture e on the fitting side is formed in a relatively large size for inserting the removing jig thereinto. If the receptacle connector 1B' is fitted in an inclined position with the plug connector 1A', the pin contact a of the receptacle connector 1B' abuts against a tip of the socket contact c to damage it or penetrates into a space between the socket contact c and the inner wall of the insert aperture e. These phenomena detrimentally affect the reliable connection between the receptacle connector 1B' and the plug connector 1A'. This results from the fact that the difference between the inner diameter of the insert aperture e and the outer diameter of the socket contact c is more than twice the thickness of the cylindrical portion of the jig.
In order to form an earth circuit for a hitherto used plug connector mounted on a main body of a machine or a control box, one end of a ground connection lead wire is connected together with a protection circuit lead wire to a ground protection circuit terminal provided on the plug connector separately from a signal terminal, and the other end of the ground connection lead wire is connected to the control box or the like by means of connector set screws.
In such a prior art, in order to form the earth circuit, the ground connection lead wire is particularly prepared and its end must be clamped to the control box together with a connector. This construction is complicated and difficult to operate. Moreover, as the earth circuit is provided only on the side of a receptacle connector, there is a risk of electric current inadvertently flowing through a worker or so-called electric shock occurring when he connects external contacts to the receptacle connector, while holding the plug connector. Therefore, this arrangement includes a problem concerning protection of human beings.